Central traffic signal control

ABSTRACT

Two lines interconnect a central traffic signal control station with a local control station. The two lines carry signals from the central station to the local station that determines whether the local station is under local or central control. When on central control, the two lines carry signals that cause the traffic signal at the local station to advance to the next condition. In addition, the system includes circuitry that establishes a predetermined interval in which the central station is conditioned to receive signals over the two lines from the local station indicative of a predetermined condition, such as the main thoroughfare signal being green so that a shift between local and central control may be effected without interrupting the smooth flow of traffic during the changeover, and so that central control may continuously monitor the operation of the local control station.

UnitedStates Patent Siklos et al.

[ 51 June 13, 1972 [541 CENTRAL TRAFFIC SIGNAL CONTROL [72] Inventors: Gregory Slklos, Bronx; James Brkudden,

3,528,054 9/1970 Auer et a1 ..340/35 Primary Examiner-William C. Cooper Anomey-Wolf, Greenfield & Sacks [57] ABSTRACT Two lines interconnect a central traflic signal control station with a local control station. The two lines carry signals from the'central station to the local station that determines whether the local station is under local or central control. When on central control, the two lines carry signals that cause the traffic signal at the local station to advance to the next condition. In addition, the system includes circuitry that establishes a predetermined interval in which the central station is conditioned to receive signals over the two lines from the local station indicative of a predetennined condition, such as the main thoroughfare signal being green so that a shift between local and central control may be effected without interrupting the smooth flow of traffic during the changeover, and so that central control may continuously monitor the operation of the local control station.

TELEPHONE LINE II CIA/I1:

- ISOLATED OPERATION REMOTE OPERATION PATENTEDJUM 13 1972 SHEET 3 BF 3 PLLIALLICLIOZLLI INVENTORS GREGORY SIKLOS JAMES B. RUDDEN BY QMflWJQfia/mufw;

ATTORNEYS o 4mm III'IIIO 0 405.200 3004 BACKGROUND OF THE INVENTION The present invention relates in general to the selective control of local traffic signals from a central location and more particularly concerns a novel system for effecting such control over an ordinary low grade telephone line that conveys information directing changeover between central and local control, advancing to the next traffic signal condition upon direction from central control and, during a predetermined limited time interval, information from the local station to the central station on the occurrence of a predetermined initial condition, such as the main thoroughfare signal being green. These features are embodied in reliably operating apparatus that is relatively inexpensive.

It has long been recognized that the flow of traffic may be improved by logically coordinating the traffic control conditions along a network of thoroughfares. An old approach involved synchronization with power lines to change the traffic signals along a thoroughfare so that a vehicle traveling at a predetermined constant speed need never stop. A fundamental difficulty with this system is that it is difficult for the vehicles to maintain this speed under conditions of traffic flow when coordination of traffic signals along a network of thoroughfares is most desirable. Accordingly, a more recent approach involves central control of a number of local traffic signals at intersections of the network of thoroughfares. Typically, central control is exercised by a computer that determines what the condition at each controlled intersection should be to maintain optimum traffic control at a given time. Yet, during periods of low traffic, or when computer control fails, it is desirable to allow the traffic signals to function under local control. Typically, such control is accomplished over more than two-wire lines or if two-wire lines are used, the flow of information is in one direction only and may involve the use of relatively costly transmission lines. If the lines are leased, the additional expense of using high quality lines and paying for leasing them when computer control is not necessary is disadvantageous.

Accordingly, it is an important object of this invention to provide methods and means for establishing communication and control between central and local control stations of a traffic signal system over two-wire lines.

It is another object of the invention to achieve the preceding object reliably over relatively poor quality lines.

It is a further object of the invention to achieve one or more of the preceding objects with equipment that is relatively low in cost.

It is still a further object of the invention to achieve one or more of the preceding objects while accepting signals from the local station only during predetermined time intervals.

SUMMARY OF THE INVENTION According to the invention, there is a two-wire transmission line intercoupling a central control station and a local traffic signal control station. Polarized signals transmitted from the central to the local station select local or central control and initiate a change in signal condition at the local control station when under control of the central station. The two wires also may carry information from the local station representative of a predetermined initial condition, such as the main thoroughfare signal having turned green; however, the central station is conditioned to receive such information only during a predetermined relatively short interval.

Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawing in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a primarily schematic circuit diagram of a typical central station control system according to one embodiment of the invention;

FIG. 2 is a primarily schematic circuit diagram of a typical local station according to the invention for association with the central station of FIG. 1;

FIG. 3 is a primarily schematic circuit diagram of a central station control system according to still another embodiment of the invention; and

FIG. 4 is a primarily schematic circuit diagram of a local station according to the invention for association with the central station of FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference now to the drawing and more particularly FIG. 1 thereof, there is shown a primarily schematic circuit diagram of a typical central station control according to the invention. A signal applied between terminals 11 and 12 to central hold and advance Kl-IOL-ADV relay l3 performs both the selection of remote control of a local station and advancing the indicated traffic conditions when the local station is remotely controlled from the central station. When relay 13 is energized, arm 14 of relay 13 couples the positive d-c potential on terminal 15 to line L1 through resistor 16. Advancing is accomplished by intermittently deenergizing relay 13 for a predetermined short time interval to produce an advancing condition at the local station while being sufficiently short, typically 180 milliseconds, so that the local station remains under control of the central station. This mode of operation will be better understood from the description hereinafter of the local station illustrated in FIG. 2.

Diode D3 passes negative pulses to operate central station KSTA relay 21 and thereby signify that the main (or A) street at the local intersection is about to be given the green signal (The cross or B street is then yellow [BY]). Typically the duration of the negative pulse applied to KSTA relay 21 is 100 milliseconds, thereby causing its arm 22 to move to the ON position and couple the negative d-c potential on terminal 23 through resistor R3 and diode D6 to operate KBY relay 24 and its contacts 25 and 26. This operation signals the computer via contact 25 that the main street is about to turn green and lights map light 27 through diode D4 and contact 26 at the central station to give a visual indication that the main street is about to turn green. Contact 26 also function as a holding contact to keep KBY relay 24 energized through diodes D5 and D6 and resistor R4 until KSTA relay 2] becomes deenergized so that arms 14 and 22 through diode D1 in effect short circuit KBY relay 24 to allow it to become deenergized.

Capacitor C2 may be charged negatively from terminal 23 with arm 22 in the ON position through diode D2 to help keep KSTA relay 21 in the operate condition until arm 14 is returned to the hold position. This additional time is largely determined by the time constant comprising the product of capacitor C2 and the resistance of resistor R2. The condition of the KSTA relay at the time the advance pulse ends determines the condition of the KBY relay until the next advance interval.

Referring to FIG. 2, there is shown a primarily schematic circuit diagram of local station circuitry suitable for use with the central station of FIG. 1..Upon the occurrence of a posi- I tive potential upon line L1 local KADV relay 31 is energized to move arm 32 to the select remote condition and thereby energize the local holding relay 33 with energy delivered through a-c plus terminal 34 after rectification by diode D6. Relay 33 operates immediately, but releases after a time interval of about 2 seconds. In the operate position its arm 35 is connected to the normally open contact so that each time local advance KADV relay 31 is released, a pulse of energy is provided from a-c plus terminal 34 through resistor 36 to render triac TR conductive and operate cam drive motor 37 to select the next desired traffic signal condition at the local intersection being controlled.

Whenever cam contact Y is open and capacitor 41 is discharged, a portion of the energy flowing through triac TRl is rectified by diode D6 to charge capacitor 41 positively upon the occurrence of an advance impulse. This charging current operates the local state KSTA relay 42 once. However, when cam contact Y is closed to help indicate the position of local equipment at the central station, capacitor 41 is charged negatively through diode 98. The occurrence of an advance impulse will then cancel the negative charge upon capacitor 41 without operating the local state KSTA relay 42. Diode 99 prevents negative current from flowing through relay 42 when contact Y is closed. Resistor 100 allows capacitor 41 to discharge back to zero volts after contact Y opens.

When relay 42 operates, arm 44 moves to a contact in series with resistor 45 and prevents the local advance KADV relay 31 from being energized while lines L1 and L2 are conditioned for the 100 millisecond duration to transmit a signal representative of the main (or A) street about ready to become green, this signal typically being coincident with the cross (or B) street being amber, designated YB. Arm 46 is operated by local hold KHOL relay 33 and receives an a-c signal when the cross street is in the amber condition, this a-c signal being rectified by the bridge circuit including D7, D8, D9 and D and other circuit components to provide a negative pulse that may be transmitted through resistor 45 and arm 44 over line L2 to operate the central KSTA relay 21 when diode D3 (FIG. 1) passes potential.

The delay properties of local hold relay 33 prevent its associated arms from being released to the local position during the short interval in which a hold signal is interrupted to signal that an advance to the next indicated traffic condition is desired. When local operation is desired, the positive signal on line L1 is interrupted. Local hold relay 33 then releases, and arm 35 carries local control signals from the local control unit 47.

Referring to FIG. 3, there is shown another embodiment of the invention which is somewhat similar to the embodiments of FIGS. 1 and 2 but additionally includes stepping circuitry that performs an additional function of readying the system for the receipt of a status signal as determined by the time when the state KSTA relay is in the operate condition. In addition the central station of FIG. 3 includes separate hold and advance relays at the central station.

One end of holding relay 51 and of central station advance KADV relay 52 is connected to positive terminal 53, the other end of each relay being selectively returned through terminals 54 and 55 respectively, typically under computer control, to minus line 55. Central station control occurs upon energization of holding KI-IOLD relay 51 to move its arm 56 down and couple positive terminal 53 through arm 57 of advance KADV relay 52 and resistor 58 to telephone line L1 to signal the local station that central control is desired while also operating stepping KSTEP relay 61 through diode D11 to open the stepping contacts 62.

The occurrence of an advance pulse operates advance KADV relay 52 to move KADV arm 57 down and momentarily interrupt the positive potential on line L1 to signify the local station that the trafiic condition should be advanced. Stepping relay 61 is characterized by a delayed release of approximately I milliseconds so that its contacts 62 do not return to the closed position until after the first 120 milliseconds of the advance interval.

If the main street is green, the local station transmits a negative pulse on line L1, typically having a duration of 100 milliseconds and occurring in the center of the advance interval. This negative pulse is passed by diode D12 to operate the state KSTA relay 63 and pull its arm 64 down so that the negative potential on terminal 55, connected to one end of the main street green KMSG relay 65, and the positive potential on terminal 53 may operate relay 65 to pull the respective arms 66, 67 and 68 down when the main street is green. One set of the contacts 66 and 67 signals the computer the other operates a map light. Contacts 68 function to hold in KMSG relay 65.

Contact 64 of relay 63 allows negative voltage 55 through diode D16 to charge capacitor C1 delaying the drop out of relay 63 until after relay KADV 52 has been released.

When the negative pulse on line Ll from the local station is not sent during the advance thus not operating state KSTA relay 63, arm 64 may then carry the positive potential from terminal 53 through arm 56, contact 62 and diode D13 to drop out KMSG relay 65 during operation of the advance KADV relay 52. Thus with this operation the main street green information can be taken from the controller G1 lamp circuit directly while other schemes require a separate circuit providing the information one step before main street green. D17, C2, C3, C4 and C5 are noise suppressors.

Referring to FIG. 4, there is shown a largely schematic circuit diagram of a local station suitable for use with the central station of FIG. 3. The local advance KADV relay 71 is operated by the positive hold potential on line L1 to move its arm 72 down and couple the a-c signal on terminal 73 through resistor 74, diode D13, resistor 75 and diode D14 to operate local Kl-IOL hold relay 76, characterized by a delayed release of about two seconds. The a-c signal on terminal 73 is also transmitted through resistor 74, diode D13 and diode D15 to local stepping KSTE relay 77 to operate that relay and move arm 81 down. Operation of local hold Kl-IOL relay 76 causes arm 82 to move down.

Upon the occurrence of an advance pulse resulting in the interruption of the positive potential on line L1, local advance KADV relay 71 releases to allow arm 72 to move to the position shown and thereby connect the positive potential on terminal 73 through arm 72, arm 81, arm 82 and resistor 84 to trigger triac TRl and operate the traffic signal cam drive motor 37.

Stepping KSTE relay 77 is characterized by a delayed release so that about 100 milliseconds after arm 72 has moved to the local and advance position indicated, KSTE relay 77 releases. lts arm 81 is then in the position indicated to carry ac energy from terminal 73 over a path including arm 72, arm 81, diode D15 capacitor 85 and resistor 86 to operate state KSTA relay 87. This relay remains operated for about milliseconds to move its arm 91 down and thereby permit a negative signal to be provided on line L1 relative to line L2 for that 100 millisecond time interval in which arm 91 is down. This negative potential is typically developed from the MSG signal applied on terminal 92 after being coupled by transformer 93 and rectified by diodes D16, D17, D18 and D19, connected in a full-wave retification circuit.

When under remote control with arm 94 of local hold KHOL relay 76 down, the signal on terminal 92 is not coupled to local state KSTA relay 87. However, when under local control, arm 94 is up as shown so that the MSG signal on terminal 92 may be transmitted through arm 94, diodes D20, D21 and resistor 86 to operate KSTA relay 87 and cause the negative signal to be delivered over line L] relative to line L2 back to the central station to signify that the main street is green.

The local station is then conveniently available for being controlled by the central station.

This arrangement is especially advantageous because it has the approval of the New York Telephone Company after having been found to operate well below their objectional noise interference level.

When under local control, local control unit 47 provides appropriate advance signals to the control electrode of triac TRl to advance cam drive motor 37 under local control. C3 and diode D22 are noise suppressors.

The invention is characterized by a number of features. It allows for full control of intersection timing from a central control station. Circuitry is free from complexity and highly reliable. Low grade telephone lines may be used for communication between the central and local stations with a resultant reduction in line rental costs. Maintenance costs are low. All these advantages are achieved with standard controllers.

There has been described a novel system for selectively exercising local or central control over traffic signals at a location remote from the central station. It is evident that those skilled in the art may now make numerous modifications of and departures from the specific embodiments described herein without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims. What is claimed is: 1. A traffic control system comprising; a central control station, at least one local traffic signal control station remote from said central control station, 7 two-wire transmission line means for intercoupling said central control station and said local traffic signal control station, said central control station having a source of polarized signals including means for supplying a signal of a first polarity across said two-wire transmission line to select central control of said local traffic signal control station, and means for removing said signal of said first polarity from across said lines for a predetermined time interval that is much shorter than a complete trafiic control cycle, said local traffic signal control station having local control means responsive to said polarized signals including means responsive to said first polarity potential across said lines for said predetermined time interval for maintaining said local station responsive to control from said central station, said local traffic signal control station having means responsive to said interruption for said predetermined time interval for producing a change in signal condition, and a source of an information signal including means for providing a signal across said two-wire transmission line of a second polarity opposite to said first polarity and only during said predetermined time interval,

said central control station having means for receiving said information signal over' said two-wire transmission line means.

2. A traffic control system as defined in claim 1 wherein said signal of second polarity is provided each time that said first polarity signal is sent except when said first polarity signal has shifted said local traffic signal control station to other than a main street proceed condition.

3. A traffic control system as defined in claim 1 wherein said means for supplying and said means for removing a signal of a first polarity comprises a relay means having at least one set of contacts associated therewith, and wherein said relay means is energized for supplying a signal of a first polarity by way of the set of contacts, and is de-energized for removing the signal of first polarity.

4. A traffic control system as defined in claim 1 wherein said means responsive to said interruption for said predetermined time interval comprises a relay means responsive to the interruption of the signal of first polarity for producing a change in signal condition.

5. A traffic control system comprising;

a central control station,

at least one local traffic signal control station remote from said central control station,

two-wire transmission line means for intercoupling said central control station and said local traffic signal control station,

said central control station having a source of polarized signals,

said local traffic signal control station having local control means responsive to polarized signals of one polarity for selectively rendering said local trafflc signal control station responsive to an interruption of said polarized signals of one polarity for a predetermined time interval for initiating a change in signal condition at the local traffic signal control station,

said local traffic signal control station having a source of a status signal,

said status signal being generated each time that said signal condition has been caused to advance in response to interruption of said polarized signal of one polarity except when said polarized signal of one polarity has advanced said local traffic signal control station to other than a main street proceed condition. 

1. A traffic control system comprising; a central control station, at least one local traffic signal control station remote from said central control station, two-wire transmission line means for intercoupling said central control station and said local traffic signal control station, said central control station having a source of polarized signals including means for supplying a signal of a first polarity across said two-wire transmission line to select central control of said local traffic signal control station, and means for removing said signal of said first polarity from across said lines for a predetermined time interval that is much shorter than a complete traffic control cycle, said local traffic signal control station having local control means responsive to said polarized signals including means responsive to said first polarity potential across said lines for said predetermined time interval for maintaining said local station responsive to control from said central station, said local traffic signal control station having means responsive to said interruption for said predetermined time interval for producing a change in signal condition, and a source of an information signal including means for providing a signal across said two-wire transmission line of a second polarity opposite to said first polarity and only during said predetermined time interval, said central control station having means for receiving said information signal over said two-wire transmission line means.
 2. A traffic control system as defined in claim 1 wherein said signal of second polarity is provIded each time that said first polarity signal is sent except when said first polarity signal has shifted said local traffic signal control station to other than a main street proceed condition.
 3. A traffic control system as defined in claim 1 wherein said means for supplying and said means for removing a signal of a first polarity comprises a relay means having at least one set of contacts associated therewith, and wherein said relay means is energized for supplying a signal of a first polarity by way of the set of contacts, and is de-energized for removing the signal of first polarity.
 4. A traffic control system as defined in claim 1 wherein said means responsive to said interruption for said predetermined time interval comprises a relay means responsive to the interruption of the signal of first polarity for producing a change in signal condition.
 5. A traffic control system comprising; a central control station, at least one local traffic signal control station remote from said central control station, two-wire transmission line means for intercoupling said central control station and said local traffic signal control station, said central control station having a source of polarized signals, said local traffic signal control station having local control means responsive to polarized signals of one polarity for selectively rendering said local traffic signal control station responsive to an interruption of said polarized signals of one polarity for a predetermined time interval for initiating a change in signal condition at the local traffic signal control station, said local traffic signal control station having a source of a status signal, said status signal being generated each time that said signal condition has been caused to advance in response to interruption of said polarized signal of one polarity except when said polarized signal of one polarity has advanced said local traffic signal control station to other than a main street proceed condition. 